In general, an acrylonitrile-butadiene-styrene (hereinafter, called ‘ABS’)-based resin is widely used to electricity, electronic parts, office machines, car parts and the like due to its relatively good properties such as impact resistance, mechanical strength, moldability, gloss and the like.
The ABS-based resin is much influenced by properties such as average particle diameter and the like of diene-based rubber latex as a rubber ingredient. For example, properties of the ABS-based resin may vary depending on average particle diameter, a gel content and a swelling index of the diene-based rubber latex.
Specifically, the ABS-based resin is commonly prepared by an emulsion polymerization method. Diene-based rubber latex is prepared by the emulsion polymerization method to provide impact strength, an aromatic vinyl compound and a vinyl cyanide compound are added thereto and subjected to graft reaction by the emulsion polymerization method to prepare an acrylonitrile-butadiene-styrene graft copolymer, and then a styrene-acrylonitrile copolymer (hereinafter, SAN) is mixed to the graft copolymer to finally prepare thermoplastic ABS resin.
In this case, the diene-based rubber polymer can be advantageously applied to the production of ABS-based resin when polymerization conversion rate reaches 90% or higher, and when the polymerization conversion rate of the diene-based rubber polymer is 90% or higher, the polymer may have a gel content of 90% to 95% and a swelling index of 14 to 20.
The gel content and the swelling index are closely related to the polymerization conversion rate and a polymerization reaction temperature. For example, in order to increase the polymerization conversion rate, polymerization is conducted at a relatively high temperature, and therefore, the gel content is rapidly increased but the swelling index is largely decreased as the polymerization conversion rate improves. When the gel content is high, transparency may be increased due to low swelling index but impact resistance may be decreased. On the contrary, when the gel content is too low but the swelling index is too high, the impact resistance may be improved but the transparency may be decreased. Thus, in order to obtain ABS-based resin having excellent properties, a diene-based rubber polymer having properly controlled a polymerization conversion rate, a particle diameter, a gel content and a swelling index is required.